It is known in the art relating to engine pistons to develop a skirt shape through various methods involving theoretical design and physical engine testing to define an acceptable shape for each engine application. It is intended to accommodate thermal growth, combustion force deformations and stiffness of the piston and its associated cylinder in operation while minimizing lateral and tilting motions of the piston that cause noise and wear. In one prior proposal, an abradable coating is provided on a piston skirt which is then run in an engine to generate the desired shape of the skirt for use in a production version of the piston.
Whatever the method of development used, it is now common in automotive vehicle engine pistons to provide a skirt having a generally ovalized configuration in lateral cross section with a major axis between the thrust and counterthrust sides. The skirt may also include a variable longitudinal profile generally having a smaller variable diameter toward the top of the skirt near the piston ring belt and a larger diameter near the bottom and having the bottom and top edge diameters slightly reduced.